?  y    nt 


Circular  No  37,  Second  Rlvise. 


•     \  I HON 


United  States  Department  of  Agriculture, 

BUREAU  OK    KNTOMOLOGY. 

L.  O.   HOWARD,   KntomologUt  and  Chief  of  Burca 


XSJ^o*'    BYDBOCYANIC-ACID    (i\s    FOB    II  HliaiiM,    t.Kl.l.v 
"  s|  s    vm)   <  oil)    FRAMES 


j  a i J-.i  in  l'.  Woods, 

'  of  Plant  Industry 


i  N  ri: i  i..\. 

fticitle  for  green] se  fumigation  is  t" 

Dacco  in  it-  rnrrr+H-^Lati^  III  many  instances  ii  is  without  doubt  the 
cheapest  and  safest  insecticide  to  use  against  aphides  and  ;i  few  other 
greenhouse  insects.  It-  effectiveness,  however,  under  the  l>e-t  <■< >i i< I i - 
tions  i-  not  great,  as  it  requires  repeated  use  ;it  short  intervals.     M 

r.  it  may  cause  serious  injury  to  the  plants.  In  the  case  of  violet- 
it  has  been  found  to  be  of  only  slight  value  against  aphides  working 
in  the  bud,  and  while  it  may  destroy  the  so-called  "  green  aphis  "  when 
exposed,  it  is  not  effective  in  killing  the  ■•In-own  aphis."  On  the 
other  hand,  tobacco  may  prove  injurious  to  the  foliage  and  0 
bringing  on  epidemics  of  "spot."  Tobacco  is  also  useless  against 
scale  insects  in  general  and  mealy  bugs.  The  desirability  of  -'Hue 
insecticide  as  easily  used  as  tobacco,  but  more  penetrating  and  effective 
and  less  likely  to  injure  plant-,  was  apparent,  and  l.r, -.uue  absolutely 
necessary  in  our  stud}  of  the  diseases  of  certain  crops. 

Hydrocyanic-acid  gas,  since  it-  introduction  by  the  Bureau  of  Ento- 
mology in  lsst''  as  a  remedy  against  scale  bisects  of  the  orange,  has 
proved  of  great  value  as  an  insecticide.  I'iv\  ious  t<>  our  experiments 
early  in  1895,  though  it  had  been  occasionally  tried  in  greenhou 
hydrocyanic  acid  was  not  recommended,  on  account  of  it-  injurious 
effects  upon  plant-.  A- a  result  of  a  series  of  careful  experiments  we 
found  that  as  a  rule  plants  were  less  injured  by  a  short  exposure  to  a 
relatively  large  amount  of  Lra-  than  they  were  by  a  long  exposure  to  a 
relatively  small  amount.     ( )n  the  other  hand,  a  strong  dose  for  a  short 

EXPLAKATOBl      NOTE.        I'll.      I'.i    t    tll;lt    :l    rirelll.-ir    of    the    ]'.ure:UI    Of    KlltiMi.. 

should  be  written  by  an  expert  of  the  Bureau  of  Plant  Industry  d Is  a  word 

splanation:  Messrs.  \.  r.  Woods  and  P.  It.  l>.T-.'tt.  who  prepared  the  I 
two  editions  Jointly,  (bond  it  necessary,  In  the  course  <>f  tlieir  Investigations  "f 
the  diseases  of  greenhouse  plants,  to  destroy  the  insects  Irving  upon  the  plants 
which  they  bad  under  observation.     For  this  purpose  they  used  hydrocyanic- 
acid  gas  and  thus  became  by  this  practical  experience  bo  well  fitted  to 
litis  particular  phase  "f  the  use  ,.f  this  Important  gas  that  I  requested  thei 
prepare  a  circular  on  this  subject    This  last  edition  has  been  revised  by  Mr. 
Woods  :it  my  request,     i..  O.   ii"  •  ird,  1 
32802    Clr.87    08    —1 


time  was  the  mosl  effective  in  killing  insects.  Different  species  and 
varieties  of  plants,  however,  were  found  to  vary  remarkably  in  their 
power  of  withstanding  the  poison.  This  in  many  cases  appeared  to 
depend  upon  the  open  or  closed  condition  of  the  breathing  pores  as 
well  as  upon  peculiarities  of  the  cell  contents.  Fumigation  an  hour 
or  two  after  sundown,  with  the  temperature  as  low  a>  practicable,  was 
round  to  give  the  best  results.  In  all  cases  the  foliage  must  be  per- 
fectly dry  or  it  may  be  injured  by  the  gas.  In  each  case  the  proper 
amount  of  gas  to  use  and  the  length  of  exposure  must  be  determined 
by  experiment.  It  is  impossible  at  present  to  give  a  general  ride  ap- 
plicable to  all  plants  in  all  stages  of  development.  "When  the  condi- 
tions are  once  determined  they  must  be  strictly  followed  to  insure  the 
greatest  success.  Methods  of  experimenting  will  be  described  in  the 
latter  part  of  thi-  circular.  The  quantity  of  pis  in  each  case  i^  al- 
ways given  in  terms  of  the  potassium  cyanide  from  which  it  is  made, 


Fig.  1. — Fumigating  bos.  showing  trays  and  coleus  cuttings.      (Original.) 

and  on  a  basis  of  a  cubic  foot  of  space,  as  will  be  explained  more  in 
detail  farther  on.  The  cyanide,  as  well  as  the  gas  made  from  it.  i> 
exceedingly  poisonous,  and  both  must  be  used  with  the  greatest  care. 


CROPS  AND  PESTS  OX  WHICH  THE  GAS  HAS  BEEX  SUCCESSFULLY  USED. 

Ferns. — ^ovDavalliamooreana  infested  with  a  scale  insect  (Chion- 
aspis  sp.),  0.075  gram  of  08  per  cent  potassium  cyanide  should  be 
used  for  each  cubic  foot  of  space  to  be  fumigated,  not  deducting  the 
space  occupied  by  the  plants.     Length  of  exposure,  twenty  minute-. 

One  hundred  and  fifty  to  two  hundred  plants  with  frond-  in  all 
stages  of  development  have  been  thus  treated  two  or  three  time-  each 
year  for  the  past  thirteen  year-  with  no  injury  to  the  plants  and 
almost  complete  destruction  of  the  insect.  They  were  treated  fifty  at 
a  time  in  a  fumigating  box  (fig.  1).  described  later. 
[Cir.  ;:tj 


Adiantum  cuneatum  and  A.  ballii  have  been  tried  on  p    mall 
and  were  not  injured  by  the  treatment. 

Coleun.  ''Golden  Beddcr,"  "  Verchaffeltii,"  "  Shylock,"  and 
others.  Twentj  four  thousand  plants  in  pol  ,  badlj  infested  with  the 
"  w  bite  tailed  "  meal}    b  '  '  The 

contained  15,587  cubic  feel  of  I  reated  :it  the  rate  of  one  tenth 

of  .1  gram  of  98  |"i-  cent  cyanide  of  potassium  per  cubic  foot  of  space 
for  twenty  minutes,  one  hour  after  dark.  Orthezia  all  killed  and 
plant-  not  injured  in  the  least.     All  other  of  destroying  the 

Orthezia  had  I n  tried  without  effect.  Large  numbers  of  the  com- 
mon mealy  bug  were  also  killed  by  this  treatment;  but  it  was  not 
nearly  so  effective  as  for  the  "white-tailed"  mealy  bug.  All  coleus 
cuttings  made  l>\    the  United   States   Propagating  Gardens   for  1 1 1*- 

past  eleven  years  have  I n  fumigated  l»  fore  being  prepared  for  the 

cutt  ing  bed  <  see  liir-  1  I. 

D&ubh  English  violet  .  "  Marie  Louise,"  "  Lady  Campbell,"  and 
other-.  For  aphides  and  general  fumigation  fifteen-hundredths  of  a 
gram  of  98  per  i  ent  cyanide  of  potassium  for  each  cubic  foot  of  space 
is  required.  The  exposure,  if  made  according  to  direction-,  will  not 
hurt  the  plant-  in  any  stage  of  growth.  Since  the  lir-t  publication 
of  tin-  circular  in  1899  the  '_ra-  has  been  used  on  a  large  scale  bj  com- 
mercial growers  in  fumigating  violets,  with  the  greatest  success,  only 
a  few  treatments  during  the  season  being  required.  Length  of  ex- 
posure, twentj  to  thirty  minutes.  Leaf  'ating  larva?,  slugs,  milli- 
pede-, cutworms,  etc.,  when  exposed  are  killed  as  well  as  aphides. 
lied  spiders,  however,  arc  not  entirely  eradicated  by  the  treatment. 
The  foliage  of  single  violets  like  (  alifornia  and  Princess  of  Wales 
are  sometimes  slightly  injured  by  the  stronger  dose  of  gas.  A  weaker 
dose  i  one  tenth  of  a  gram  potassium  cyanide  per  cubic  foot  i  should 
be  used  W  hen  they  arc  to  be  treated. 

Other  plants.  Other  plant-  on  which  tin"  gas  ha-  Keen  tried  on  a 
small  scale  indicate  that  it  ma\  probably  have  quite  a  wide  range  of 
usefulne 

A'"-  i.  "  Perle  des  jardins,"  "  Mermet,"  and  "  Bride."  The  young 
growth  on  roses  is  particularly  sensitive  and  has  been  more  or  less 
injured  in  all  our  experiments. 


1  'I'll.  !   en   the   I  'ith   L'fain 

of  cyanide  per  cubic  f""t  of  space  for  twenty  minutes  without  injury.     Further 
experiment,  however,  Is  neces  ommended  for 

these:    Idiantum   ballii;  Adiantum  runpatum;    llornna   macrorl  fjaia; 

Inthuriumci'i/stallinum:    Iralla  ftlicifnlia  nrium  intybu* ; 

o/or;  Crotons  (in  variety);  Dieffenbachia  i>iuii<ini;  Eichhornia  */«< - 
■isiii.i:   Fuchsias   (In   variety);     Hoffmannia   refutgi 
randa    orotifolia;    Marantas    (in    variety);     \  candidistima,    odorata, 

ami  rosea;  Panax  rictoria';  Pandanun  veitchii;  Phrynium   varicgatu 
Ihiiiin  limit  nii:  Yanthosoma  Hndeni. 
[Cti 


Carnations. — Scott,  Garfield,  .Meteor,  and  McGowan  will  stand  one- 
tenth  of  a  gram  98  per  cent  cyanide  per  cubic  foot  of  space  for  15  min- 
utes without  material  injury.  This  will  kill  about  90  per  cent  of  the 
aphides,  hut  will  not  kill  thrips.  The  use  of  the  gas  for  carnations 
need-  to  he  more  carefully  investigated  before  it  is  recommended. 
The  same  is  true  of  chrysanthemums;  on  which  it  has  been  tried  with 
only  partial  success,  the  young  growth  being  very  sensitive. 

Grapes  under  glass. — The  gas  has  been  used  with  success  in  New 
Zealand  '  for  mealy  bugs  (Dactylopius  adonidum  L.)  at  the  rate  of 
one-third  of  an  ounce  98  per  cent  cyanide  to  100  cubic  feet.  This  i> 
equivalent  to  nine-hundredths  gram  per  cubic  foot.  The  gas  is 
liberated  after  dark  and  left  in  till  next  morning,  when  thorough 
ventilation  is  given.  It  largely  escapes,  however,  during  the  night. 
The  treatment  is  said  not  to  injure  the  plants  in  the  least. 

Tomatoes. — Dr.  Jabez  Fisher,  in  "American  Gardening"  (Oct.  -J'.K 
1898),  reports  using  the  gas  for  "  white  fly  "  (Aleyrodes  vaporarioinin 
Westw.)  on  tomatoes.  The  gas  from  1  ounce  of  pure  cyanide  of 
potassium  for  each  1,000  cubic  feet,  left  in  the  house  over  night,  killed 
all  the  insects  without  injury  to  the  plants.  This  method  has  not 
yet  proved  successful  with  us  in  any  case,  but  it  should  nevertheless 
receive  careful  trial  by  other  experimenters. - 

CUBIC    CONTENTS    OF   THE    HOUSE. 

It  is  necessary  in  every  case  to  determine  with  great  care  the  cubic 
contents  of  the  house,  frame,  or  box  in  which  the  fumigation  is  to  be 
made.  To  illustrate:  Fig.  -1  shows  cross  sections  of  two  styles  of 
greenhouse  structures  now  in  general  use.  At  the  left  is  an  even  span 
house  100  feet  long,  1'2  feet  wide,  2  feet  on  the  side>.  and  5  feet  0 
inches  from  the  surface  of  the  beds  to  the  ridge,  with  a  walk  1-t  inches 
wide  and  15  inches  deep.  To  determine  accurately  the  number  of 
cubic  feet  in  this  or  a  house  of  similar  construction  :  First .  make  a 
rough  drawing  showing  a  cross  section  of  the  house:  second,  divide 
the  space  into  triangles  and  rectangles  by  drawing  a  line  connecting 
the  two  wall  plates  and  one  from  the  ridge  at  right  angles  to  this; 
mark  on  each  its  resepective  length  in  feet  and  inches.  Compute  the 
number  of  cubic  feet  in  each  of  the  rectangles  and  triangles  in  accord- 
ance with  the  following  method.  In  the  even  span  house  shown  at 
the  left  the  number  of  cubic  feet  of  space  in  the  walk  is  found  by  mul- 

Fourth  Report,  Dept.  of  Agr.,  New  Zealand.  1S96.  Pp.  141-143. 
■See  also  Fumigation  Methods,  by  W.  <;.  Johnson  (Orange  Judd) ;  Violet 
Culture,  by  Galloway  (Florist  Exchange);  Hemenway,  II.  D. — Bui.  22  n.  s., 
Div.  Ent.,  I".  s.  Dept.  Agric,  pp.  69-78,  1 : « « • :  Chittenden,  F.  II.— Rid.  ll.  n.  s.. 
Div.  Env..  U.  S.  Dept.  Agric,  pp.  20-26,  1901  [Cir.  37  quoted];  Morrill,  A.  X.— 
Cir.  57,  Bur.  Ent..  U.  S.  Dept.  Agric,  pp.  5-9,  1905. 
[Cir.  ::t] 


tiplying  the  width  bj  the  depth  by  the  length,  thus:  Multiply  I  fool 
•_'  inches  bj  I  fool  •"■  inches  by  I""  feel  ;  reducing  to  inches  we  have  l  I 
inches  multiplied  h\  l"«  inches  \>\  1,200  inches  equals  252,000  cubic 
inches;  dividing  tin-  result  bj  1,728,  the  number  of  cubic  inches  con 
tained  in  a  cubic  foot,  we  have  L45.83  cubic  feet.  The  rectangle 
A  1)  <i  F  is  computed  in  the  same  way,  except  that  in  this  case  it  i- 
not  necessan  to  reduce  the  feel  to  inches.  Ii  would  be  12  feel  multi- 
plied by  •_'  feel  l>\  100  feel  equals  2,400  cubic  feet.  This  brings  us  to 
the  triangles.  The  rule  generally  given  for  calculating  the  area  of  a 
right-angle  triangle  is  to  multiply  the  base  by  the  perpendicular  and 
divide  tit*.*  product  bj  2.  The  resull  multiplied  by  1 1 1 « -  length  of  the 
house  will  give  the  number  of  cubic  feel  the  triangular  portion  con- 
tains. For  example,  taking  the  triangle  A  ('  I'.:  6  feel  multiplied  by 
8  feel  6  inches,  equals  21  feet,  divided  by  2  equals  10.5  feet,  multi- 
plied by  100  fee!  equals  1,050  cubic  feet.  The  mi-cm  of  the  triangle 
E  C  D  and  the  cubic  feet  in  this  part  of  the  house  are  determined  in 


Fig.   -. — End  section  of  even  span   house  nt   left,   same  of   three-quarter   span   h" 

right     (Original.) 

the  same  way;  or,  in  this  case,  since  the  triangles  are  equal,  tin'  de- 
sired result  i-  obtained  by  multiplying  the  number  of  cubic  feet  in  the 
triangle  A  ('  E  by  •_':  L,050  multiplied  by  •_'  equals  2,100  cubic  feet. 
Thf  contents  of  thi-  house  is  therefore  ll">.s:>  pin-  2,400  pin-  2,100, 
equals  1,645.83  cubic  feet;  thi-  result  multiplied  by  the  required  dose 
per  cubic  foot  of  space  will  give  the  amount  of  cyanide  of  potassium 
necessary  for  one  fumigation. 

Fig.  •_'  shows  Mt  the  right  a  cross  section  of  a  three-quarter  span 
house  LOO  feet  long,  Is  feet  wide,  front  wall  1  feet  I  inches,  back  wall 
6  feet  4  inches,  and  11  feet  in  inches  to  the  ridge.  The  cubic  contents 
of  thi-  house  i-  determined  in  the  -Mine  manner,  except  that  the  two 
triangles  being  unequal,  each  one  will  have  to  be  calculated  separately. 
Th»>  house  contains  15,050  cubic  feet.  It  will  thus  !><•  seen  thai  the 
cubic  contents  of  a  house  or  frame  of  any  style  ran  be  readily  deter- 
mined by  simply  dividing  a  cross  section  of  thf  same  into  tin-  i 
82892  -Ctr.87— 4X 2 


6 

sary  number  of  triangles  and  rectangles  and  calculating  as  demon- 
strated above. 

A  simpler  method  of  obtaining  the  cubic  contents  of  a  house  has 
been  described  by  Galloway.  This  consists  in  laying  off  a  cross  sec- 
tion of  the  house  according  to  scale,  on  a  piece  of  paper  ruled  in 
squares,  each  square  being  equal  to  a  square  foot.  For  example,  sup- 
pose the  squares  are  one-eighth  of  an  inch  to  a  square  foot.  The  end- 
section  of  the  house  is  then  accurately  laid  off  on  these  square-,  and 
by  counting  the  squares  and  parts  of  squares  the  number  of  square 
feet  of  space  in  the  end  section  can  be  easily  determined.  This,  mul- 
tiplied by  the  length  of  the  house,  will  give  the  cubic  contents  in  cubic 
feet. 

AMOUNT  OF   POTASSIUM    CYANIDE   TO   USE. 

After  the  number  of  cubic  feet  in  the  space  to  be  fumigated  is  deter- 
mined, the  amount  of  cyanide  required  is  found  by  multiplying  the 
cubic  contents  by  the  dose  per  cubic  foot.  For  example,  if  single 
violets  are  to  be  fumigated  the  dose  would  be  one-tenth  of  a  gram  per 
cubic  foot.  A  dose,  therefore,  for  the  even-span  house,  containing 
4.i'>4Cp  cubic  feet,  would  be  4,646  multiplied  by  .1  equals  404.0  grants. 
To  reduce  this  to  ounces,  divide  the  number  of  grams  by  28.35  (the 
number  of  grams  in  an  ounce  avoirdupois).  464.6  divided  by  28.35 
equals  16.38  ounces  avoirdupois.  It  may  be  necessary  to  reduce  the 
fraction  of  ounces  to  grains:  437..")  (the  number  of  grain-  in  an  ounce) 
multiplied  by  .38  equals  100  grain.-. 

If  double  violets  are  to  be  fumigated  the  cubic  contents  would  be 
multiplied  by  .1">.  thus:  4,646  multiplied  by  .15  equals  696.9  grams, 
divided  by  28.35  equals  24.58  ounces  avoirdupois.  .58  ounce  equals 
253  grains.  In  the  case  of  a  small  space  of  less  than  150  cubic  feet 
the  dose  in  grams  should  first  be  determined,  and  this,  if  necessary, 
can  be  changed  to  grain-  by  multiplying  the  number  of  grams  by 
15.43  (grains  in  a  gram),  thus:  30  (cubic  feet)  multiplied  by  .15 
gram-  equals  4.5  grams,  multiplied  by  15.43  (grain-  in  a  gram)  equals 
69.435  grains,  or  approximately  09.5  grains.  The  reduction  to  oui 
or  grains  will  not  be  necessary  if  metric  weight-  are  used,  which  is 
strongly  urged.  When  the  dose  for  certain  plants  in  a  given  house, 
frame,  or  box  is  once  obtained,  it  should  be  carefully  recorded  on  the 
house  or  box  thus : 

Contents:  1,015  cubic  feet. 

r  Ferns,  .075  gram  per  cubic  foot  equals  Tti.l  grams. 

\  Violets,  double,  at  .IT.  gram  per  cubic  foot  equals  lo'i.L'o  grams. 


If  a   scale   weighing  with  avoirdupois  weights  is  used,  the  dose 
d  be  r< 

[Cir.  37] 


should  be  recorded  in  ounces  and  grain? 


-IIM    riNG    v    I  I  M  l     l"    ll    M 10 ATE. 

Care  should  be  taken  i<>  select  a  night  when  the  houses  can  he  ven- 
tilated (lir  required  nine  without  injury  in  the  plants  ami  when  there 
i-  no  likelihood  of  rain. 

PR]  PARA  [TON   hi     I  in     HOUSE  FOR  FUM  tO  v  I  ION. 

On  account  •>!  the  very  poisonous  nature  of  the  gas,  it  is  necessary 
to  arrange  a  number  of  ventilators,  the  more  tin-  better,  -<>  that  they 
rail  l>e  easily  opened  from  the  outside.  It  would  he  very  dangerous 
to  enter  the  house  while  it  contain-  the  gas.  All  broken  glass  should 
l>e  replaced  and  hole-  stopped  up;  a  thoroughly  we1  piece  of  news- 
paper will  close  a  crack  effectually  or  take  the  place  of  a  broken  glass 
it'  necessary.  It  is  best  not  to  permit  the  gas  i"  gel  into  lire  pit-  or 
engine  room-:  these  should  he  cut  oil'  from  the    pace  to  be  fumigated. 

In  case  of  a  large  range  of  houses  opening  into  each  other,  it  i-  best 
to  separate  them  into  several  sections,  by  tacking  up  building  paper  or 
oiled  cloth  -o  that  each  section  may  he  fumigated  separately  and  at 
different  time-.  Theworkmay  thus  be  done  with  great  ease  and  care. 
and  with  less  danger  to  the  plant-.  Great  care  must  he  exercised  to 
have  tin-  foliage  of  the  plants  to  he  fumigated  /»  fifth/  <//;/.  Leaves 
or  stems  which  have  moisture  on  them  will  be  injured. 

The  temperature  of  the  houses  should  be  aboul  60c  I'.  The  gas  is 
more  active  and  more  likely  to   injure  the  plant-' at    high  temperature-. 

\l  1   rHOD    '  »]      MAKING    T1IK    (.  v>. 

The  material-  required  are  98  per  cent  cyanide  of  potassium,  broken 
into  -mall  lump-,  besl  secured  in  I"  or  •_'.">  pound  can-  at  •"><>  to  |<>  cents 
a  pound,  and  commercial  sulphuric  acid  at  :'.  to  I  cent-  a  pound  by 
the  carboy. 

For  an  ordinary  house  or  frame,  good  vessels  for  liberating  the  gas 
are  U  or  2  gallon  earthen  jars  of  a-  -mall  diameter  a-  possible  SO  as 
to  insure  the  immersion  of  the  cyanide  of  potassium  when  it  i.-, 
dropped  into  the  acid.  On*'  jar  should  he  used  to  about  every  •!'<  feci 
ill  length  of  such  houses  a-  described,  in  order  that  the  gas  may  he 
quickly  distributed  when  set  \v-v.  When  the  jar-  are  placed  in  posi- 
tion the  next  step  is  to  arrange  to  lower  paper  bags  containing  the 
desired  amount  of  cyanide  into  the  jars,  from  the  outside.  This  i- 
U'-t  done  by  passing  a  cord  through  a  hook  or  -crew-eve  attached  to 
the  roof  over  each  jar  in  such  a  manner  that  when  the  -trii 
strings  are  loosened  from  the  outside  the  hair-  of  cyanide  will  he  low- 
ered into  their  respective  jar-,  a-  shown  in  Wc  •">.  When  the  strings 
are  ready,  divide  the  amount  of  cyanide  to  he  used  into  part-  corre- 
[Clr.87] 


8 

sponding  to  the  number  of  jars.  Wrap  each  part  up  in  a  single 
thickness  of  ordinary  newspaper  and  put  in  ordinary  brown  paper 
baas,  and  attach  the  bags  to  the  strings,  as  shown  in  fig.  3.  While 
the  jars  are  empty  test  the  arrangement  to  see  if  it  works  satisfac- 
torily. After  each  bag  is  suspended  in  place,  the  other  end  of  the 
string  securely  fastened  where  it  can  be  reached  from  the  outside, 
and  the  arrangement  tested,  move  the  suspended  bags  to  one  side  so 
they  will  be  out  of  the  way  while  putting  the  water  and  acid  in  the 
jars.  When  this  is  done,  pour  into  each  jar  an  amount  of  water 
about  equal  to  the  bulk  of  the  potassium  cyanide  in  the  bag.  Eight 
ounces  of  cyanide  will  require  about  half  a  pint  of  water.  The  sul- 
phuric acid  should  then   be  poured   in  until   steam   rises   from  the 


Fig.  3. — Violet  house  prepared  for  fuiuigatiou.     y Original,  j 

water.  This  would  require  for  a  pint  of  water  about  a  pint  and  a 
half  of  acid.  It  is  not  necessary,  however,  to  measure  the  acid,  as  the 
evolution  of  steam  indicates  when  the  right  amount  has  been  poured 
in.  Always  put  the  water  in  first  and  then  pour  in  the  acid.  As 
soon  as  this  is  done  place  the  bags  over  their  respective  jars.  When 
all  is  ready,  go  out,  close  the  door,  and  carefully  loosen  the  strings, 
allowing  the  bags  to  settle  into  the  acid.  While  the  method  just  de- 
scribed is  desirable  for  a  large  house  or  series  of  houses  from  which 
exit  would  be  difficult  after  dark,  it  is  not  necessary  to  go  to  the 
trouble  of  lowering  the  cyanide  into  the  acid  by  strings  in  most 

[Clr.  37] 


cases.  When  the  jars  containing  the  water  and  acid  are  properlj 
placed,  the  cyanide  in  the  paper  sacks,  as  previously  described,  may 

lie  -et  beside  the  jars;  then  il perator,  starting  in  « nn-  end  of  the 

bouse,  may  carefully  drop  the  bag  into  the  water  and  acid,  coming 
out  the  other  end  of  the  house.  It  there  are  i w <>  sets  of  jara  in  ili ffer 
fiii  paths,  it  will  !'»'  necessary  for  two  operators  t'»  start,  one  in  each 
path,  working  in  tin'  same  direction,  at  about  the  same  rate  of  speed. 
In  this  way  tin'  cyanide  can  be  placed  very  quickly  and  easily  in 
quite  m  large  series  <>!  jars,  taking  care  that  no  cyanide  i-  placed  in  a 
jar  in  Midi  a   way  a-  to  cut   oil'  the  exit    from  tin'  house  >>(  any  oper 

ator.     Tin-  method  of  hand  dropping  is  now   tl ne  most   largely 

used.  Tlir  gas  will  very  soon  be  given  oil'  and  Oil  every  portion  of 
thf  house.  It  i-  colorless  ami  smells  ami  tastes  like  peach  pit-.  A 
little  of  it  i-  harmless,  but  too  much  will  cause  death.  A  small  quan- 
tity will  leak  out  of  the  house;  avoid  positions  where  it  can  be 
smelled.  The  time  of  exposure  should  lie  reckoned  from  the  lower- 
ing of  tin'  cyanide  into  the  jar-.  When  the  proper  time  has  elapsed, 
varying  lor  different  plants  as  previously  stated,  quickly  open  the 
ventilators  from  thf  outside,  so  that  the  gas  can  escape  a-  rapidly  as 
possible.  It  will  all  lif  "mm'  from  a  large  house,  such  as  described 
in  this  circular,  in  half  or  three-quarters  of  an  hour,  and  the  ventila- 
tors may  then  be  closed,  if  necessary.  Next  morning  thf  material 
left  in  thf  jars  should  be  emptied  into  a  hole  ami  buried.  It  is 
nothing  hut  sulphate  of  potash,  sulphuric  acid,  ami  water,  having  a 
little  hydrocyanic  acid  gas  in  solution.  Thf  latter  will  soon  dis- 
appear and  thf  sulphuric  acid  will  unite  with  lime  in  thf  soil,  form- 
ing gypsum. 

II   kflGATINO    BOXES. 

For  the  purpose  id'  experimenting  ami  where  only  1  few  hundred 
plant-  are  to  be  treated,  a  tight  box  ma\  be  made  of  30  to  50  cubic 
feel  capacity.  The  box  should  he  a-  nearly  air-tight  as  possible,  with 
a  removable  cover  and  a  -mall  door  at  the  bottom  for  introducing  the 
cyanide  of  potassium  into  the  howl  containing  water  and  sulphuric 

aeid.  a-  shown  in  fig.   1. 

The  wire  tray-  shown  in  tne  same  illustration  are  used  in  fumigal 
ing cuttings  of  coleus  or  other  plants  When  desired  the  t ray-  can  he 
removed  and  pot  plant-  -ei  in  the  bos  and  given  such  fumigation  as 
desired.  To  prevent  injury  to  the  plant-  they  should  be  so  set  that 
the  foliage  tloe-  not  come  within  Is  inches  of  the  bowl  near  the  -mall 
door.  When  the  plant-  are  arranged  the  top  i-  put  on  securely  and  a 
little  water  i-  poured  into  the  howl,  and  then  sulphuric  acid  i-  added 
till  steam  i-  formed.  The"hecessary  amount  of  cyanide,  wrapped  in  a 
small  pieee  of  newspaper,  i-  then  dropped  into  the  howl  and  the  little 
I  fir.  :;7l 


10 

door  quickly  closed.  When  the  desired  length  of  time  has  elapsed 
take  off  the  cover  and  open  the  door  and  retire,  so  as  not  to  breathe 
the  gas.     In  a  few  minutes  the  gas  will  have  sufficiently  escaped  so 

that  the  plants  may  he  taken  out  and  other-  treated  in  the  same  way. 
Injury  (if  there  is  any)  to  the  plants  may  not  -how  for  two  or  three 
day-,  so.  in  the  case  of  experimenting,  conclusions  should  not  be  has- 
tily drawn.  The  box  may  be  used  in  the  daytime  if  the  work  is  done 
in  a  cool  place.  For  experimental  purposes  and  treating  plants  on  a 
small  scale,  a  small  greenhouse  containing  L,000  cubic  feet,  or  Less,  is 
better  than  a  box,  as  the  results  obtained  with  it  are  more  reliable 
and  there  i-  less  danger  of  injury  to  the  foliage. 

CONDENSED    DIRECTIONS. 

(1)  Carefully  determine  the  cubic  content-  of  the  house  and  the 
amount  of  cyanide  of  potassium  to  use. 

(•_')    Make  the  house  as  tight  as  possible. 

(3)  Arrange  so  that  the  ventilator-  can  he  opened  from  the  out- 
side. 

(-1)    Place  the  jars  and  strings  in  position.1 

(  5)  After  dusk  attach  the  hags  containing  the  cyanide  to  string-,  as 
described,  and  find  if  they  work  correctly. 

( •', )  Hang  the  hags  to  one  side  and  put  water  and  acid  into  the  jar-  : 
arrange  protection  and  put  the  hags  in  place  again. 

(  7 )  When  all  is  ready  lower  the  hags  into  the  jars  by  loosening  the 
strings  from   outside. 

(8)  After  the  proper  exposure  open  the  ventilators  from  outside, 
leaving  them  open  from  thirty  to  forty-five  minute-  before  entering 
the  house. 

(9)  Next  morning  bury  content-  of  the  jars. 

(10)  The  foliage  must  be  perfectly  dry. 

CAUTION. 

It  should  be  remembered  that  hydrocyanic-acid  gas  is  one  of  the 
deadliest  poisons  known  fatal  to  human  beings  and  plants,  as  well  as 
to  insects. 

Greenhouses  which  are  within  50  to  75  feet  of  dwelling-  should  not 
he  fumigated  unless  the  windows  and  doors  of  the  latter  on  the  side 
next  to  the  greenhouse  can  he  closed  during  the  operation. 

'If  the  potassium  cyanide  is  to  be  dropped  into  the  jars  by  band,  place  the 
package  beside  each  jar:   then  a    man   i'm  each   separate  group  of  jars  should 
start  at  one  end  and  work  towards  the  end  from  which  quick  exit  can  be  made. 
After  proper  exposure  open  ventilators,  etc. 
[Cir.  :S7] 


Ii  is  essentia]  thai  the  exact  proportion  of  cyanide  be  1 1 -< •>  1  mi  the 
rate  designated  for  each  cubic  fool  of  space  and  thai  the  exposure 
should  iint  exceed  the  limit  ascertained  l>\  experiment  as  appropriate 
in  the  plant-  to  be  fumigated.  \  great*  r  trength  "I  gas  >>r  a  longer 
exposure  than  specified  is  apl  i"  result  in  injur}  i"  the  plant 

It  is  besl  to  it-''  tin-  method  at  first  experi ntall}  on  a  small  scale 

before  attempting  the  fumigation  of  an  entire  greenhouse,  and  a  pre- 
liminary  test  should  always  be  made  in  case  plants  "l  a  sped 
variety  not  previously  fumigated  are  to  be  treated. 

A  | >| >t  <  >\  ed  : 

.1  \  MEfl    \ \ "  1 1  SON, 

n  tm  ii  of  .1  grit  ulturt . 
Washington,  D.  ('..  March   ',.  /> 

U'l, 


O 


UNIVERSITY  OF  FLORIDA 

lllllllillWIlllllll 

3  1262  09216  4523 


